Generator of electrical oscillations



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g A Rwy W m, mm R. HARDY 9 GENERATOR OF ELECTRICAL OSCILLATIONS Filed July' 16, 1946 2 Sheets-Sheet 2 1N Vi/V7 A2; 5 ME HARD) Patented May 30, 1950 UNITED STATES PATENT OFFICE GENERATOR OF ELECTRICAL OSCILLATIONS France Application July 16, 19516, Serial No. 684,047 In France June 27, 1942 Section 1, Public Law 690, August 8, 1946 Patent expires June 27, 1962 2 Claims. 1

My invention relates to a generator of electrical oscillations and more particularly to circuit arrangements for generating oscillations having a high degree of stability and in which the effect of the variation of the supply voltages is necligible. This type of oscillation can be especially used with the so-called sawtooth voltage generators, which are employed in sweeping, scanning or analyzing devices in connection with television systems or cathode-ray oscillograph tubes.

In such apparatus, the displacement of the spot is obtained by means of two saw-tooth voltages, of differing frequencies which are applied to two rectangular, deflecting systems that efiect the scanning of the surface of the screen in the form of juxtaposed lines.

By using discharge tubes, thyratrons, gas tubes, etc., there is provided a relaxation circuit which consists in a slowly charging condenser, that abruptly discharges when the charge voltage has attained one certain magnitude, which allows the gas tube to trigger and the charging process begins again. The working of these devices depends in a high degree upon the supply voltage and if the latter is not duly stabilized, this causes large variations of the frequency. Thisdrawback is overcome to a great extent, especially in television by synchronizing the discharge by means of the so-called synchronizing impulses which aid the trigger eifect of the tube at every discharge.

Owing to the instability of the frequency, it it necessary to apply a synchronizing impulse at every discharge; otherwise the difference would increase rapidly.

One of the objects of my invention is to provide circuit arrangements which have little need of synchronizing impulses, or at least, which maintain a stable frequency approximating much more to isochronism than the ordinary, well known circuits do.

The invention will be described with reference to the accompanying drawings in which- Figure 1 shows representative curves of sawtooth voltages:

Fig. 2 represents a schematic arrangement of a stable oscillator according to one form of my invention; and

Fig. 3 is a simplified circuit diagram of an oscillator arranged according to my invention for producing a saw-tooth voltage.

The auto-oscillating devices-which comprise such oscillating circuits as made of inductances and capacities connectedto amplifying tubes, as well as, for instance the resistance' capacity circuits where successive charges and discharges characterize the frequency--are subjected to high instability due to the more or less simultaneous modification or variation, through time, of many elements having a direct relation with the frequency of the device. Thus, for instance, it is well known that with a triode valve oscillator provided with tuned inductances in the grid and plate circuits, the frequency depends upon many factors, i. e. not only upon the inductance and the capacity alone, but upon the internal tube resistance and the supply voltages as well.

For stabilizing the frequency, there are utilized such elements as, for instance, piezo-electric quartz crystals or tuning-forks, that is, resonators which are little influenced in their vibrations by the variations of the voltages and of the connecting elements.

With such stabilizing contrivances, there remain other material conditions, as conditions of temperature for instance, which have to be observed.

With relaxation circuits, a quartz crystal may be used for insuring the synchronization or for making the discharge nearly independent of the variations of voltage; this would lead to more complicated circuits and, furthermore, the quartz would not allow for an easy modification of the frequency through a progressive adjustment or within suiioient limits of variation.

The device of my invention which is to be hereinafter described permits of maintaining a great stability of the oscillating circuits which may directly produce saw-tooth voltages that are utilizable foroscillographic sweeping systems and may as well produce voltages of a very different form, either sinusoidal or not, and throughout much elongated frequency ranges, retaining at the same time the possibility which the quartz does not possess, or allowing for an easy variation of the frequency, and the improved means being also less expensive than with the quartz.

Several forms of oscillations may be produced, according to the method of my invention; that on the saw-tooth principle will beconsidered, in a non-restrictive sense, the described being applicable to scanning systems for television receivers and the like.

In Figure 1, saw-tooth voltages are shown, which are used for instance for displacing the spot of a cathode ray tube ina television receiver. These oscillations are generated by a discharge tube and circuits arrangements with gas tubes for example.

At a certain magnitude e, point M on OZ determines after a time T, the end of a line and the release of the rapid discharge MN.

d: or d4 with a time difference A at every tooth. This difierence will be characterized on thescreen by a deformation of the image which will be all the more important if it is repeated as many times in the same direction.

A difference At of /500 in the scanning of an image having 500 lines would give after one image,

a deformation which it is easy to conceive, trans- ,T, which are a consequence of the variations of the supply voltage.

Should it be now another possible consequence of voltage variations considered, with circuits that .are differently designed and wherewith the discharge would occur after a time T but independently of the magnitude as, there would re- .sult a variation A6 in amplitude, that is in the length of the lines described by the spot instead of the variations At in frequency.

The practical result would be on image X a deformation which cannot be perceived by the eye if Ae is also /500. This would be shown by -a reduction of /500 of the width of the image. vBut as in a television receiver, the vertical scan-- ,ning would be also submitted to /500 of variation,

the image would finally be reduced by /500 in every dimension, that is practically unchanged.

If with At the image becomes unobservable with Ae it remains stable.

In the application of the invention to the scanning of oscillograph tubes, it is possible to make the deformations a function of Ae alone and keep A1; at a negligible value.

Fig. 2 schematically represents an oscillator constituting a saw-tooth generator.

A condenser C is placed in series with a resistance R across the terminals of a source of high voltage, which allows the slow charging of the condenser C.

For the sake of simplification, R is here shown as a resistance, but it could be a pentode for obtaining a load with a constant current.

At a given time, there is applied, at the terminal A, which is connected to an electrode that --controls the electron current of tube V2, an impulse of a short duration.

The valve V2 is so arranged that, in the absence of impulses, the internal resistance thereof of capacity C which is connected in parallel with the anode circuit of V2.

During the impulse, the capacity C is practically short-circuited by V2 and discharged.

will take place the next discharge of C which will then allow a new impulse to pass through V1 and L2 foracting again at the end of the next cycle on V2 and the phenomenon will recur on and on, having for cadence the transmission time of the delay line L2.

Here it is to be seen that as peculiarity of this process, the impulse passing through V1 and La is not amplified by going again through V1 and afterwards L2 again, but it is a new impulse of a definite form, independent from the form in which the original impulse was released.

It is a very important feature of my invention.

If a closed circuit should be designed, by causing 'the same impulse to travel, an auto-oscillator would be obtained, where the impulse would be soon deformed and the phenomenon would assume another character.

The impulse generated by the discharge of C will always have, on the contrary, a characteristic form and it will be capable of releasing a new discharge at the end of a time period which depends upon L2, during which C again begins to be charged through R in series.

It would be possible to use, instead of RC, any other device, such as inductances which could be coupled or not, and with or without capacity; the main point being to release a phenomenon giving rise to a signal which it is possible to discriminate and thereafter utilize for controlling a release after a given duration.

Also, the delay network or line L2 is not the 1 only means for producing the delay in the transvery high and does not disturb the charging.

When the impulse is ended, C is charged again.

But the quick discharge of C through the valve V2 has given rise to a strong current in a short lapse of time and it results therefrom that an impulse may be collected and directed onto a valve V1, which has as loading impedance a transmis-.

. valve V2.

When this impulse will have travelled through the delay line L2 and will have reached V2, there mission of the trigger signal and every other known device can be employed, e. g. transmission lines, resonating devices, or devices transmitting vibrations where a time difference elapses between the instant when a phenomenon occurs and when it is sent back, deformed or not.

For instance, in the case of an artificial line, it appears, quite obviously, that the arrangement can be'embodied, if not as a transmission through line L2, but with a line or system transmitting the vibration that operates on the echo principle, that is by reflecting the signal towards the inlet terminals where it is introduced in the line.

If, in the diagram of Fig.2, there is used a line with intermediate tappings, it will be possible to choosetransmission times t1, t2, is, which characterize different frequencies of the saw-teeth.

It will stillbe possible to use a line having a progressive variation of the transmission time, or again two or more successive lines, one roughing out the frequency, the other or others permitting of finishing up the adjustment.

It is to be observed that if the voltage supply of R varies, the magnitude of the discharge impulse can also slightly var as well as the width thereof- These two variations are negligible for durations of impulses which are short relatively to the transmission time of the delay circuit L2 and they do not influence the frequency. It is quite the case of the conditions of variation of the Ae form (and not At) which have been set forth hereinbefore abovel Fig. 3 represents the simplified circuit diagram permitting of producing the scanning lines on the screen of a cathode ray oscillograph tube, for instance for television purposes.

The terminal. B is connected to the deflecting elements of the tube. The condenser C is charged in series with the pentode V2. The potentiometer P4. permits of adjusting the time of the charging; that is to say, the speed with which the spot moves on the screen of the tube. Thevalve V1 is connected in parallel and short-circuits 0 when its grid is positive; it allows the charging of C when its grid is very negative. Between the cathode of V1 and the ground, and connected in series, a resistance R1 of a small value is placed.

This cathode is connected through condenser C1 to the control grid of the tube V3, which grid is connected by Rs with the negative terminal of a suitable polarizing source P3. The plate voltage of this tube is constant. The delay network L2 is terminated at its two ends by its iterative impedance. Its input-end is connected with the cathode of the said tube V3 and with the cathode of a triode V4, on the grid of which are impressed periodic impulses. This triode acts as an impulse amplifier. The delay network or line L2 is provided at its input-end with taps not shown, respectively connected with its first sections, which provides, by switching operations, the eifect of a transmission time equal to the period of the spots parallel displacements on the screen of the cathode-ray tube.

At the beginnin of an image, for instance, an impulse goes through A and V4, next through L2 and C2 and causes for a short moment the grid of V1 to become positive in such manner that C is discharged and begins thereafter a sawtooth operation.

During the quick discharge of C, an impulse has resulted therefrom at the terminals of R1 and this discharge impulse has been brought on to V3, then through L2 and, at the end of a time T corresponding to the duration of one line, it causes anew the discharging of C.

The cycle proceeds and one single impulse at the beginning of the image is enough for starting the scanning.

At every line or saw-tooth, it is feasible to send at A a synchronizing impulse, but this does not seem necessary since actually the system is made independent of frequency perturbations through the use of a device L2, the transmission time of which is invariable with respect to the voltages or tubes of the circuit. Therefore it is possible to transmit for instance the 500 lines of one image and to synchronize only once per image by sending to A a strong impulse at every image beginmng.

The effect produced by the synchronizing impulse at A is a correction of the eventual difierenc of frequency which could have occurred for an insufficiently precise adjustment of L2.

The line L: is shown as fixed in the drawing, but it will be understood that every adjusting system may be used for modifying the transmission time T.

The length of the scanning lines will be controlled for instance by the bias of the grid of the loading pentode by means of potentiometer P4.

Every other means may be employed for injecting the controlling or synchronizing impulse, either at the entry of L2, or at the output thereof, or at V1. Likewise, tappings may be used on line L2, as well as more complicated circuits for rendering shorter or modifying the form of the synchronizing or controlling impulse or of that issued from the discharge of condenser C.

It will also be understood that one may use, instead of C and V2, every other means of charge and discharge for producing saw-tooth voltages or voltages of another form; there is, for instance, contemplated the use of coupled inductive circuits which are connected to the discharge tube, so that during the discharge, this valve oscillates or tends to oscillate under control of these circuits; this is intended for accelerating the discharge or for producing one or several oscillations for the duration of the discharge that have a well defined form and frequency.

It is also contemplated to produce instead of saw-tooth voltages, sinusoidal voltages and means for multiplying these frequencies so as to produce, for instance by means of an oscillator of kilocycles, according the above exposed principle, sinusoidal, multiple or submultiple voltages, either by multiplying, or by synchronizing with the proposed oscillator one or more secondary oscillators of sub-multiple frequencies.

While I have described my invention in certain of its preferred embodiments I realize that modifications may be made and I intend no limitations upon my invention other than may be imposed by the scope of the appended claims.

What I claim is:

1. In a saw-tooth voltage generator, in combination: a, capacitor, one of whose electrodes is grounded, a thermionic vacuum tube having a cathode, a control grid and an anode, a resistance connecting said cathode to said grounded electrode, a connection connecting said anode to the other capacitor electrode, a direct-current supply with constant voltage Whose negative terminal is grounded, a saturated pentode having a cathode, a control grid, a plate and a pair of auxiliary grids, connections connecting the positive terminal of said direct-current supply to the anode of said thermionic vacuum tube through the electrodes of said saturated pentode, means to adjust the control grid voltage of said pentode, a delay network, means connecting the output terminal of said network to the control grid of the vacuum tube and one of its input terminals to the ground, image-impedances terminating this network at its input and output terminals, an amplifier tube having a. cathode, control grid, and a plate, means for negatively biasing said last mentioned contro1 grid, a capacitive connection connecting said last mentioned control grid to the cathode of said vacuum tube, a connection connecting the cathode of said amplifier tube to the ground through the input image-impedance, means for producing current pulses, and a connection connecting the output terminal of said last mentioned means to the cathode of said amplifier tube.

2. In a saw-tooth voltage generator as set forth in claim 1, in which said means for producing current pulses comprises a pulse amplifier vacuum tube, having a constant voltage anode, and a, negatively biased control grid connected to the output of a positive valtage pulse generator, whose period is a multiple of the delay time of the said network, and a connection connecting the cathode of said pulse amplifier tube to the cathode of the other amplifier tube.

RENE HARDY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,180,364 Norton Nov. 21., 1939 2,212,173 Wheeler et a1. Aug. 20, 1940 2,212,420 Harnett Aug. 20, 1940 2,281,948 Peiplow May 5, 1942 2,413,063 Miller Dec. 24,, 1946 

